1. Field of the Invention
The present invention relates in general to a method and an apparatus for transmitting and receiving signals in a video phone, and more particularly to a method and an apparatus for transmitting and receiving a voice signal simultaneously with a video signal via a single transmission line in the video phone.
2. Description of the Prior Art
Generally, there has been employed a telephone line as a transmission line in a video phone.
FIG. 1 is a block diagram of a generic construction of a conventional apparatus for transmitting and receiving signals in the video phone employing the telephone line. As shown in the drawing, the conventional apparatus comprises a camera 1 for taking an image of a caller, an A/D converter 2 for digitizing a video signal outputted from the camera 1, a first memory unit 3 for storing an output signal from the A/D converter 2, a modulator 4 for modulating the signal, or digitized video signal, stored in the first memory unit 3, a first amplifier 5 for amplifying an output signal from the modulator 4 by a predetermined amplification degree, a second amplifier 8 for amplifying a digitized video signal from a counterpart by a predetermined amplification degree, a demodulator 9 for demodulating an output signal from the second amplifier 8, a second memory unit 10 for storing an output signal from the demodulator 9, a D/A converter 11 for converting the signal, or digitized video signal from the counterpart, stored in the second memory unit 10 into an analog signal to output the analog signal, or video signal to a monitor 12, a control circuit 14 connected between the first and the second memory units 3 and 10 and the A/D converter 2, for feeding desired address and control signals to them, a standard telephone 7, and a switching circuit 6 connected among an output terminal of the first amplifier 5, an input terminal of the second amplifier 8, the telephone 7 and a telephone line 13, for selectively connecting the output terminal of the first amplifier 5, the input terminal of the second amplifier 8 or the telephone 7 to the telephone line 13 in accordance with some conditions.
The operation of the conventional apparatus with the above-mentioned construction will now be described.
The image of the face of the caller, taken by the camera 1, is an analog signal, which is converted by the A/D converter 2 upon receiving a clock from the control circuit 14, into a digital signal to be stored into the first memory unit 3. Also, the control circuit 14 feeds address and control signals to the first memory unit 3. Data stored in the first memory unit 3 is modulated suitably to a line characteristic by the modulator 4 and then is transferred through the first amplifier 5 to the switching circuit 6, which sends the data out over the telephone line, thereby enabling the video signal to be sent to the counterpart.
On the other hand, upon receiving the image data, or digitized video signal, from the counterpart, the switching circuit 6 transfers the digitized video signal to the second amplifier 8, as a receiving amplifier, and then to the demodulator 9. The demodulated signal from the demodulator 9 is stored into the second memory unit 10 under the control of the control circuit 14 and the signal stored in the second memory unit 10 is then converted by the D/A converter 11 into an analog signal to be displayed on the monitor 12. Thus, the caller can see the face of the counterpart through the monitor.
FIG. 2 is a detailed circuit diagram of a part P including the telephone 7 and the switching circuit 6, shown in FIG. 1. As shown in the drawing, upon pushing a transmitting switch 15 under the condition that the caller would like to send his image to the counterpart while the caller telephones a message to the counterpart, a controller 16 outputs a control signal to a switch 17. A terminal c of the switch 17, having been connected to a terminal b during voice telephone call, is thus connected to a terminal a to send the video signal out to the counterpart via the telephone line 13, similarly to the case that the counterpart would like to send his image to the caller.
Namely, the terminal c of the switch 17 is connected to the terminal a in the transmission and reception of the video signal, while to terminal b in the voice telephone call. As a result, no transmission and reception of the voice signal can be performed under the condition of the transmission and reception of the video signal.
Referring next to FIG. 3 which is a circuit diagram of an embodiment of the conventional apparatus for transmitting and receiving signals in the video phone employing the telephone line, the conventional apparatus is shown to comprise a transmitting transformer 18 connected between the standard telephone 13 and telephone 7, for interfacing the video signal to be transmitted, a receiving transformer 19 connected between the standard telephone 13 and telephone 7 for interfacing the video signal to be received, a first video signal processing circuit 20 for processing the video signal to be transmitted, a second video signal processing circuit 21 for processing the video signal to be received, a relay 22 including two relay switches 22a and 22b, for operating to send only one of the voice signal and the video signal via the telephone line 13, and a controller 23 for applying a drive control signal to the relay 22 and the first and the second video signal processing circuits 20 and 21. In the drawing, the reference numeral 24 designates a surge voltage absorbing triac, R1 to R7 resistors and C1 to C7 capacitors.
The operation of the conventional apparatus with the above-mentioned construction will now be described.
When, normal times, the caller is to telephone a message to the counterpart, one lines L2 and T2 of the telephone line 13 and the telephone 7 are connected directly to each other and the other lines L1 and T1 are connected via the transmitting transformer 18 to each other, in order to send the voice signal to the counterpart, thereby allowing the telephone call. On the other hand, the relay 22 is driven under the control of the controller 23 and states of the relay switches 22a and 22b therein thus are changed to short lines T1 and T2 of the telephone 7, thereby preventing the voice signal from being sent to the counterpart. As a result, it is impossible to send the voice signal to the counterpart.
The controller 23 then operates to control the first video signal processing circuit 20 to send the video signal via the telephone line 13.
On the other hand, the controller 23 operates to control the second video signal processing circuit 21 to receive the video signal, even in the reception of the video signal from the counterpart, similarly to the case of the transmission of the video signal.
With the above-mentioned construction, however, the conventional apparatus cannot transmit and receive the voice signal simultaneously with the video signal via the single transmission line in the video phone, thereby resulting in the stand-by status of the one side in the course of transmission of the video signal from the other side. In result, the transmission and reception of the video signal between the caller and the counterpart by the conventional apparatus as stated above takes too much time.